tetravalent

Tetravalent is an adjective used in science to denote something that has a valence of four or is capable of forming four chemical bonds. In chemistry, it most often describes atoms that can form four covalent bonds with other atoms, typically because they possess four valence electrons. The classic example is carbon, whose tetravalence underpins organic chemistry and enables a vast diversity of compounds. Silicon and germanium, in the same group of the periodic table, are also described as tetravalent and form four bonds in many compounds. Other elements can be tetravalent in certain oxidation states, such as titanium, tin and lead in the +4 oxidation state.

In structural chemistry and materials science, tetravalent elements can form four-coordinate networks, as in silicate minerals or many metal oxides and semiconductors.

In biology and medicine, the term is used in a different sense: a tetravalent vaccine is designed to protect against four serotypes or strains of a pathogen, for example dengue vaccines that target all four dengue serotypes.

In genetics, tetravalent can refer to a structure containing four paired chromatids (a tetrad) or to the pairing interactions of four homologous chromosomes during meiosis in polyploid organisms.

Etymology: from Latin tetra-, four, and valent-, valence or capacity to form bonds.